U.S. Pat. No. 2,772,723 issued Dec. 4, 1956 to Jack B. Tunnell for SPRING UNIT FOR PLATFORM ROCKING CHAIR discloses the spring holder with which this invention is specifically concerned. The spring holder of this invention is called a mounting bracket in the Tunnell patent. The mounting brackets in the spring unit described in the Tunnell patent were specifically designed to withstand the stress imposed by resistance of opposed coil springs to elongation upon rocking movement of the chair.
The mounting brackets in the Tunnell spring unit successfully withstand the forces imposed on the spring unit by the rocking motion of the chair, but difficulty has been encountered in stabilizing the connection of the Tunnell spring units to the chair and to the platform. The force exerted by the vertically reciprocating rocking motion of the chair imparts laterally reciprocating motion to the Tunnell mounting brackets, and to the spring holders of this invention. The lateral motion is forceful and causes the sharp ends of the prior art mounting bracket to gradually wear away the wood at the points of attachment and loosen the connection of the steel mounting brackets to the wooden base and wooden platform.
The prior art mounting bracket has edge flanges at each end which extend laterally and terminate in sharp ends flush with the attachment face of the mounting flange. When operatively installed on a platform rocking chair the sharp ends of the edge flanges bear against the wooden chair or the wooden platform. It is the sharp ends of these edge flanges that dig into and wear away the wood.